Researchers are continually searching for new methods to treat and dispose of waste materials. Finding a cost-effective, environmentally safe method of dealing with waste has always been problematic, and the problem is particularly acute in large cities and other areas with high population densities. In such areas, the value of land tends to be rather high, adding significantly to the capital costs of providing a proper waste disposal site. Operational costs associated with transporting the waste, however, may offset the capital cost savings gained by moving the waste to a remote location where land values are lower. This is particularly true in the case of waste water, primarily because the cost of building and maintaining a waste water pipeline between the city and a distant location often vastly outweighs the cost savings associated with the land itself. Accordingly, it would be desirable to provide a reliable, cost efficient method for transporting waste water from one location, such as a city, to another location, such as a rurally located treatment facility.
Waste materials, including both solid wastes and waste water, represent significant potential sources of energy. Some municipalities have attempted to recover this energy and reduce the amount of solid waste deposited in landfills by incinerating solid waste. However, such garbage incinerators are meeting increased resistance due to their high cost and the risks they impose to the environment.
As an alternative to incineration, others have used anaerobic decomposition, i.e., decomposition in a low oxygen or oxygen-free environment, as a means of treating organic waste on a small scale. The main products of anaerobic decomposition include carbon dioxide (CO.sub.2), methane (CH.sub.4), hydrogen sulfide (H.sub.2 S), and nitrogen-rich solids. As methane is a primary component of natural gas and is readily combustible, methane produced by anaerobic decomposition of waste can be burned to produce energy without posing any significant environmental hazard such as those presented by common incinerators. Furthermore, the nitrogen-rich solids which are produced in this type of decomposition tend to be dispersible in water and may be used as a fertilizer or soil conditioner. Because anaerobic decomposition is an environmentally safe method for utilizing the energy stored in waste materials and because this process can provide a valuable fertilizer source, it would be desirable to have a method of utilizing this natural biochemical process on a large scale.
It has long been known that the growth rate of plants generally bears a proportional relationship to the concentration of carbon dioxide in the ambient atmosphere--a low carbon dioxide concentration tends to stunt the growth of the plant while an elevated carbon dioxide concentration can significantly increase the rate at which the plants grow. Although enhanced carbon dioxide concentration has been used in enclosed environments, such as greenhouses, utility of this technique in growing plants under field conditions is rather limited because the carbon dioxide becomes diluted by the ambient atmosphere and is blown away by the wind. Accordingly, it would be desirable to provide a means of utilizing enhanced carbon dioxide concentration to grow plants, such as trees, under field conditions.